I have just noticed some mold on the ceiling. This has not been a problem in the past as we had plenty of air leaks in the house. Now the house is so tight we have to be careful. Setting up the fan should not be a problem but making sure we are just taking the air/moisture from the bathroom is a concern. If we put in a fan then turn it on, the way it is now it appears that it would be drawing air from other parts of the house as well as the bathroom. Thank you for the links, very informative. Neither of them spoke about air flow but did mention that a fan should be on for 20 minutes after a shower to fully rid the room of moisture. Is our question about fresh air possibly not a concern? As to quality, when we got our whole house fan, we ended up spending more than we expected but got a very well made unit and are happy with it. Is there a difference in brands ? You mentioned Broan. I checked out the Broan website. My goodness. And a few other sites. I read that one CAN put this fan in/above the shower. Interesting. I believe that we would like a timer w/this, do not need a light, more than likely not a heater. Any other options we should be thinking about? The room is 182 sq. ft. This post was edited by nancyk on Mon, Jan 28, 13 at 10:24

Get a bathroom fan timer. that is the best way to get maximum air exchange without having a high power fan that sounds like a jet or costs a fortune. I am with commenter Toronto on considering inflow UNLESS you have central heat/ac bathroom, in which case air to replace the exhausted air will freely come in from the register. If you want optimum airflow in addition to fan CFM: a) you also should check your ducting if it is old, and make sure it has no obstructions b) make sure your install well mating fan with your ducting. c) get a fan timer in your switch (about $20 to $25). these can bused to insure that the fan remain on for ten or 15 minutes AFTER the users leave. It is when bather s leave, that the room has the highest relative humidity and water that needs to be evaporated and exhausted. Turning off the fan that that point is the worst thing. My advice. - insure you have register or window you can crack, if not have a cut made across bottom of your bathroom door. - Get/keep moderate fan rated 6 to 8 exchanges per hour - Get a fan timer. 15 minutes of fan after you exit is better than massive exchanges while shower is running. - check any/all bathroom fans once a year for dust. vacuum them out. if you feel low performance maybe occurring check duct and mating of fan TO duct.

If you're not trying to be 'defiant' of our reasoning, you're certainly trying to convert us to your way of thinking, and I don't think it's going to happen. Clearly you are not open to this idea, but others may at least consider it. So far the inspectors have not said anything. I consulted with two of them, the city engineer, my contractor, and fan suppliers before doing it. Firstly, I'm not going to contradict a building code, especially when there's no discernible logic (ok you disagree but fail to impart what actual advantage your system offers) or advantage to it. I'm not going to run to the library immediately to check the code, but I do get there reasonably often and will check. Again, the inspectors who are familiar with the code are okay with my installation. It could be that a fan is not required simply because I have ventilation into the room via the AC ducting and/or a window, so whether I have a fan in the room is my call. You mentioned your area does have mould issues....(as do all areas I guess) - your system is particularly unwise due to that. You are creating an unnecessary hazard. There seems to be no mold issues in the southwestern deserts or the Rocky Mountains. Our weather is heavily influenced by the Gulf of Mexico so we have humidity in the summer. I don't think it is going to be a problem but is certainly is an issue. Definitely not a hazard. You may even have created a fire hazard You're being alarmist. Explain to me how my house catches fire because the bathroom doesn't vent to the outside. There are a couple advantages to my system. First the fan draws only dry air into it. This keeps the wet dust from collecting on the fan blades and reducing the fan efficiency to near zero in a few months. Second, the fan is mounted 24 inches above the floor in the bedroom. If I need to clean it, which I doubt I will anytime soon, its right there at knee level instead of overhead on the ladder. Third, the air at 24 inches is blown up to the ceiling in the adjacent bathroom 9 inches down from the 9-foot ceiling. As you pointed out, warm air rises. My system blows relatively cool and dry air in a the ceiling height to thoroughly mix the warm/moist air with cool/dry air to get a more uniform air temp and moisture throughout the room. Fourth, air sucked into a fan is only sucked extremely locally. Without a few classes in aero I can't really get into how that works, but you'll notice the exhaust of a jet engine, or even an electric fan for that matter, can be felt much farther away from the blades than the intake air induction can be felt. You have to hold your hand directly to the back of a fan to feel any air intake at all. My system, even with a diffuser at the opening into the bathroom, blows the air into the room hard enough that I can feel it against the far wall, thus ensuring thorough air stirring and mixing. Fifthly (?), in the winter humidity is not a problem here. In the summer it can be if your AC is not properly designed. Mine seems to be but this room has not endured an entire summer. Actually spring is slightly worse for humidity because the humidity is up but the temps are not warm enough to trigger the thermostat. In the summer the AC runs day and night as the outside temps sometimes don't come down into the 80s for several days at a time. It's rather like 'vacuuming' or should I say reverse vacuuming, a room by blowing it all out with compressed air. There may be something about that system you like, but you're just taking the dust from one room (read humidity and bathroom smells) and spreading it throughout the rest of the house. And your vacuum system sucks dust in from outdoors and blows it all over the house. Which is better - the dust you already have indoors or the new dust your vacuum system is sucking in? I knew which fan you were talking about, but I was way off on my house fan power specs. Apologies. I'm not sure what model of blower I was looking at but mine is 3/4 horsepower - more like under 500 watts versus the 750 watts used by my directed fans. If one of my little fans wears out, I have backup. If my furnace fan wears out, it's a service call and a $12,000 AC system (mine is ready to be updated). Your bizarre method and logic may make the condensation evaporate more rapidly (or so you may think) because you are encouraging it to evaporate I guess into a larger area, however, that capacity would diminish over time, since the overall humidity will increase to the point of what is it - equilibrium? Where the air will hold no more moisture, and condensation begins to reform. This is where the structural damage sets in, mould forms and it becomes an unhealthy environment. From a heat transfer point of view, you need to watch your terms better to make that make sense but I think I know what you were trying to say. Still, the last sentence is the important one. The humidity increase from a shower is unlikely to saturate the 18,000 cubic feet of air in the house. However, this is exactly what I'll be looking for in the summer. These bathrooms are at the far end of the house. The concern is getting that air moved out of the confines of the bedrooms and out to the AC air intake in the living/dining rooms. I don't think it will be a problem in the summer with the AC on all the time, but we'll see. I'm more afraid of freezing my butt off in the shower with all that dry air coming in on me. I may have mentioned that I do not get any condensation in my bathroom now and I do not get any even when the fan is off. The reason for that is not clear. I'm working on the theory of massive tile heat sink where the moisture is actually condensing on the cooler tile but there is so much tile that I'm not noticing it. But there is never any fog in the bathroom and no condensation on the mirrors. Ceiling fans may have their drawbacks and I don't love cleaning them either, but I think I'd prefer them to a bunch of fans sitting around on the floors Clearly I'm not going to change your mind on that either but I have convinced several friends to use floor fans, especially in the winter, to mix the hot air at the ceiling with the cold air on the floor. Suddenly my short friends can get warm and my tall friends don't have cold feet. If the thermostat is at 5 feet off the floor and you're 5 feet tall, you live in a world where all the heat is above your head no matter what you set your thermostat to. But if you're six feet tall or taller, your face is always hot and your feet are always cold. With the little fan on the floor pointed at the ceiling behind the sofa, the air mixes in the entire room and everyone is comfortable. Everyone I demonstrate this effect to is amazed. A ceiling fan can be reversed and pointed at the ceiling, but you get into the problem again of the air intake being at 8 feet off the ground blowing air up to the 9-foot level. You really have to have the fan honking to blow that air to the walls and down. Then people seem to complain about the wind in the room. My little fans simply punch a localized hole in the thermal layers and mix them up. I keep ignoring the indelicate subject of bathroom odor, because that does not seem to be a problem in my household. It must be all the lard in the tamales down here ;-) Actually my wife pumps the veggies and fruit into us - I'm not a dietitian. Sorry I'm getting so wordy. Maybe this will stop now that we realize we're not going to change each other's minds.

No attic access? No way to get up there at all? Not a ceiling scuttle hidden in a closet some where?Agree with Joe, we can give guidelines to install the fan, but the wiring is the issue. Do you have a plan for wiring the fan? Probably the easiest would be to extend the wiring from the bathroom ceiling light. Attic access would make it a heckuva lot easier. But barring any out of the ordinary attic framing, extending the ceiling light circuit could be done with a couple of fishing tapes. Is that an option? And then...there are wall exhaust fans. Again, depending on location, electrical would be an issue.